In cellular phones, the development of thin stylish portable devices having sound functions such as music reproduction or hands-free as commodity values has been actively conducted. In this regard, there is increasing demand for electro-acoustic transducers that are made small and thin and that has a high-quality sound. As means to respond to the demand, piezoelectric electro-acoustic transducers using a piezoelectric element as a driving source have been developed. Since the piezoelectric electro-acoustic transducers use a self-expansion and contraction motion of the piezoelectric element, the piezoelectric electro-acoustic transducers are thinner than electrodynamic electro-acoustic transducers constituted by a magnetic circuit.
At present, various types of electro-acoustic transducers have been proposed (Patent Document 1).